1. Field of the Invention
The present invention relates to a liquid-crystal display device and more particularly, to a liquid-crystal display device applicable to display equipment for a notebook-sized personal computer, a car navigation system, or the like.
2. Description of the Prior Art
FIGS. 1A and 1B schematically show the configurations of a conventional Liquid-Crystal Display (LCD) device. As shown in FIGS. 1A and 1B, this conventional LCD device includes a liquid-crystal panel 203, a backlight unit 209 fixed apart from the panel 203, and a driver circuit unit 208 provided outside the panel 203. The backlight unit 209 emits backlight 215 toward the panel 203. The driver circuit unit 208 sends driving signals to the panel 203 generated-by driver circuits through lines 218.
The panel 203 has a first transparent-glass substrate 202 and a second transparent-glass substrate 204 fixed to be opposite to and apart from the first substrate 202 by a sealing member 205. A space is formed by the first and second substrates 202 and 204 and the member 205 between the substrates 202 and 204. The space is filled with liquid crystal 211.
On a surface of the first substrate 202 on the opposite side to the backlight unit 209, transparent pixel electrodes (not shown), Thin-Film Transistors (TFTs) (not shown), storage capacitors (not shown), signal lines 210, scanning lines (not shown), connection lines 201, and terminal areas 207A, 207B, 207C, 207D, and 207E are formed.
The pixel electrodes, the corresponding TFTs, and the corresponding capacitors constitute individual pixels of the display area 203a of the panel 203, which are arranged in a matrix array within the display area 203a. The connection lines 201 are located outside the display area 203a. The terminal areas 207A, 207B, 207C, 207D, and 207E are also located outside the display area 203a. The terminal areas 207A, 207B, and 207C are formed at an end of the first substrate 202, which are used for electrically connecting the signal lines 210 to the driver circuit unit 208. The terminal areas 207D and 207E are formed at another end of the first substrate 202, which are used for electrically connecting the scanning lines to the driver circuit unit 208.
The signal lines 210 are arranged at regular intervals to extend vertically in FIG. 1A. The signal lines 210 are electrically connected to the sources of the corresponding TFTs, respectively. On the other hand, the scanning lines are arranged at regular intervals to extend horizontally in FIG. 1A. The scanning lines are perpendicular to the signal lines 210. The scanning lines are electrically connected to the gates of the corresponding TFTs, respectively. The pixel electrodes are electrically connected to the drains of the corresponding TFTs, respectively.
The TFTs are located at the respective intersections of the signal lines 210 and the scanning lines.
A third part of the signal lines 210 are electrically connected to the terminal area 207A through the corresponding connection lines 201. A Tape Carrier Package (TCP) 206A including a driver Integrated-Circuit (IC) chip (not shown) therein is mounted on the terminal area 207A. The IC chip is electrically connected to the corresponding signal lines 210 and is driven by the driver circuit unit 208 through the corresponding line 218.
Another third part of the signal lines 210 are electrically connected to the terminal area 207B through the corresponding connection lines 201. A TCP 206B including a driver IC chip (not shown) therein is mounted on the terminal area 207B. The IC chip is electrically connected to the corresponding signal lines, 210 and is driven by the driver circuit unit 208 through the corresponding line 218.
The remaining third part of the signal lines 210 are electrically connected to the terminal area 207C through the corresponding connection lines 201. A TCP 206C including a driver IC chip (not shown) therein is mounted on the terminal area 207C. The IC chip is electrically connected to the corresponding signal lines 210 and is driven by the driver circuit unit 208 through the corresponding line 218.
A half part of the scanning lines are electrically connected to the terminal area 207D through the corresponding connection lines 201. A TCP 206D including a driver IC chip (not shown) therein is mounted on the terminal area 207D. The IC chip is electrically connected to the corresponding signal lines 210 and is driven by the driver circuit unit 208 through the corresponding line 218.
The remaining half part of the scanning lines are electrically connected to the terminal area 207E through the corresponding connection lines 201. A TCP 206E including a driver IC chip (not shown) therein is mounted on the terminal area 207E. The IC chip is electrically connected to the corresponding signal lines 210 and is driven by the driver circuit unit 208 through the corresponding line 218.
On an opposite surface of the first substrate 202 in the sides near the backlight unit 209, a polarizer plate 213 is fixed.
On a surface of the second substrate 204 in the side near the backlight unit 209, a transparent common electrode 212 is formed to be opposite to the pixel electrodes on the first substrate 202.
On an opposite surface of the second substrate 204 in the opposite side to the backlight unit 209, a polarizer plate 214 is fixed.
Next, the operation of the above conventional LCD device is explained below.
A constant voltage is applied to the common electrode 212 of the liquid-crystal panel 203 during the operation. Signal voltages and scanning voltages, which correspond to the image information to be displayed and which is sent from the driver circuit unit 208, are applied to the respective pixel electrodes. The signal voltages are sent through the TCPs 206A, 206B and 206C, the corresponding connection lines 201 to the TCPs 206A, 206B and 206C, and the signal lines 210. The scanning voltages are sent through the TCPs 206D and 206E, the corresponding connection lines 201 to the TCPs 206D and 206E, and the scanning lines.
The effective voltages applied across the respective pixel electrodes and the common electrode 212 cause the change in optical transmittivity of the liquid crystal 211 at the corresponding locations to the pixel electrodes dependent upon the optical characteristics of the liquid crystal 211. The change in optical transmittivity of the liquid crystal 211 leads the change in optical strength of the backlight 215 on the opposite side of the liquid-crystal panel 203 to the backlight unit 209.
Thus, the image is displayed in the display area 203a of the panel 203.
With the conventional LCD device as shown in FIGS. 1A and 1B, as seen from FIG. 1A, the TCPs 206A, 206B, and 206C are not arranged equally or uniformly with respect to the display area 203a of the panel 203. Therefore, the connection lines 201 corresponding to the TCP 206A, which extend radially from the terminal area 207A, have different lengths. For example, the resistance of the first to (n/3)-th connection lines 201 corresponding to the TCP 206A varies according to the broken line A1 shown in FIG. 7.
Similarly, the connection lines 201 corresponding to the TCP 206B, which extend radially from the terminal area 207B, have different lengths. The resistance of the (n/3)+1!-th to (2n/3)!-th connection lines 201 corresponding to the TCP 206B varies according to the broken line A2 shown in FIG. 7. Further, the connection lines 201 corresponding to the TCP 206C, which extend radially from the terminal area 207C, have different lengths. The resistance of the (2n/3)+1!-th to n-th connection lines 201 corresponding to the TCP 206C varies according to the broken line A3 shown in FIG. 7.
As a result, the resistance of the adjacent (n/3)-th and (n/3)+1!-th connection lines 201 located at the interface between the TCPs 206A and 206B varies drastically. Similarly, the resistance of the adjacent (2n/3)-th and (2n/3)+1!-th connection lines 201 located at the interface between the TCPs 206B and 206C varies drastically.
The resistance difference between the adjacent two connection lines 201 causes the effective voltage difference, thereby changing drastically the optical transmittivity of the panel 203 at the interface between the adjacent two TCPs. If the change of the optical transmittivity is equal to 2% or more with respect to the total optical transmittivity, a man is able to sense and recognize this change as luminance unevenness on the display area 203a. This leads to degradation of the display quality.
The threshold value of the resistance difference between the adjacent two connection lines 201 at which a man is able to recognize the luminance unevenness is equal to approximately 200 .OMEGA..
The above explanation about the TCPs 206A, 206B, and 206C is applicable to the remaining TCPs 206D and 2O0E for the scanning lines.
Although the connection lines 201 are formed to extend along straight lines in FIGS. 1A and 1B, they may be formed to be bent like cranks.
To solve the problem of the luminance unevenness, an improved configuration as shown in FIGS. 2A and 2B was developed, which was disclosed in the Japanese Non-Examined Patent Publication No. 5-72563 published in March 1993.
The improved configuration includes first to n-th connection lines. However, only first to third connection lines 301a, 301b, and 301c are shown in FIGS. 2A and 2B for the sake of simplification of description.
In FIGS. 2A and 2B, first to third connection lines 301a, 301b, and 301c are formed on a glass substrate 302. The first line 301a has a width of W1 and a length of L1. The second line 301b has a width of W2 and a length of L2. The third line 301c has a width of W3 and a length of L3. Similarly, the n-th line has a width of Wn and a length of Ln.
The lengths and the widths of the first to n-th connection lines have a relationship of EQU L1/W1=L2/W2=L3/W3=. . . =Ln/Wn (1)
This relationship (1) means that the first to n-th connection lines have the same resistance. Therefore, the improved configuration is able to substantially delete the effective voltage fluctuation applied to the respective pixel electrodes, resulting in the image with no luminance unevenness.
With the improved configuration disclosed in the Japanese Non-Examined Patent Publication No. 5-72563, however, the following problem will occur.
Specifically, since the ratios of the length and width of the first to n-th connection lines are designed to be the same, the problem of the luminance unevenness can be solved. However, there is a possibility that an extremely narrow connection line and/or an extremely narrow gap between the adjacent two connection lines is generated.
For example, when the first connection line has a length L1 of 10000 .mu.m and a width W1 of 20 .mu.m, and the hundredth connection line has a length L100 of 2000 .mu.m, the hundredth connection line needs to have a width W100 of 4 .mu.m. Such extremely narrow line tends to cause open-circuit or disconnection, thereby decreasing the fabrication yield of the LCD device.
If the narrowest connection line is designed to be comparatively wide in order to prevent the open-circuit or disconnection of the connection lines, the gap between the comparatively wide connection lines becomes narrow. This results in the tendency of short-circuit of the connection lines.